1. Field of the Invention
The present invention relates to a corneal surgical apparatus for incising the cornea of an eye of a patient in a layered form at the time of a keratorefractive surgery or the like.
2. Description of the Related Art
In recent years, attention has been focused on LASIK (laser in situ keratomileusis) surgery for effecting keratorefractive treatment wherein after a flap is formed by incising a corneal portion with a thickness of 150 .mu.m ranging from the corneal epithelium to the corneal stroma with one end of the cornea remaining connected like a hinge, the corneal stroma is cut away or ablated in a refractive correction amount by excimer laser light, and the flap is then returned to its original position. In this LASIK surgery, a corneal surgical apparatus called a microkeratome is used to incise the cornea in a layered form.
A typical microkeratome includes a suction ring to be vacuum-fixed to a part of the cornea ranging from a corneal ring portion to the surface of the conjunctiva, a cornea applanating member for applanating the cornea flatly, and a blade linearly or rotatively moved in the direction toward the hinge while being oscillated in the lateral direction so as to incise the flattened cornea into a layered form with a substantially uniform thickness. During the corneal incision, the cornea is likely to escape due to the movement of the blade, and therefore a certain degree of corneal rigidity is required. To meet this requirement, some microkeratomes employ such a method that the suction pressure applied to the interior of the suction ring is heightened to increase the intraocular pressure of the patient's eye, thereby obtaining the corneal rigidity.
Another method has been proposed in which the cornea applanating member is designed to have a higher friction coefficient or the cornea applanating member is provided with a suction port to suck the corneal upper surface (i.e. the flap-forming side of the cornea) while applanating the same, thereby increasing the resisting force of the cornea against the advance of the blade.
However, the former method may cause an adverse effect on the optic nerves since this method relies on the high intraocular pressure created by increasing the suction pressure applied to the interior of the suction ring.
Further, if the vacuum-fixation of the suction ring is not sufficient, or a suction tube or the like is clogged with a foreign object, there are cases where the air pressure in the space between the patient's eye and the suction ring fails to be set in a sufficient negative pressure, or the air pressure rises (the pressure tends to rise toward the positive pressure) during the surgery. As a result, a problem arise in that the corneal rigidity of the patient's eye fails to be enhanced sufficiently, which makes the incision impossible, or even if the incision is possible, the cut surface becomes nonuniform.
In contrast, the latter method is advantageous in that the intraocular pressure of the patient's eye need not be increased since the escape of the cornea from the blade can be suppressed even if the suction pressure applied to the suction ring is lowered. This method, however, suffers from another problem in that the flap is cut off in the course of the surgery, or the cut surface becomes nonuniform since the applanation and suction of the corneal upper surface by the cornea applanating member increases the frictional force between the flap and the blade in association with the advance of the blade during incision.